The present invention relates to building materials, and, more particularly, to a method for making lightweight blocks formed of aerated concrete.
Autoclaved aerated concrete is a high-quality, load-bearing, as well as insulating building material produced in a wide range of product sizes and strengths. The material has been used successfully in Europe and is now among widely used wall building materials in Europe with increasing market shares in other countries. Aerated concrete is a steam cured mixture of sand or pulverized fuel ash, cement, lime and an aeration agent. High pressure steam curing in an autoclave produces a physically and chemically stable product with an average density being about one fifth that of normal concrete. The material includes no-connecting air cells, and this gives aerated concrete some of it its unique and advantageous properties. Aerated concrete enjoys good strength, low weight, good thermal insulation properties, good sound deadening properties, and has a high resistance to fire.
Aerated concrete may be used in panels or individual building blocks. It has been used for residences; commercial, industrial and agricultural buildings; schools; hospitals; etc. and is a good material in most all climates. Panels or blocks may be joined together using common mortar or thin set glue mortar or adhesive. Aerated concrete has durability similar to conventional concrete or stone and a workability perhaps better than wood. The material can be cut or sawn and readily receives expandable fasteners. Aerated concrete has a thermal conductivity six to ten times better than conventional concrete. The material is also non-rotting, non-toxic and resistant to termites.
As disclosed in U.S. Pat. No. 4,902,211 to Svanholm, for example, aerated concrete may typically be produced as follows. One or several silica containing materials, such as sand, shale ashes or similar materials, as well as one or more calcareous binders, such as lime and/or cement, are mixed with a rising or aeration agent. The aeration agent typically includes aluminum powder which reacts with water to develop hydrogen gas at the same time a mass of what can be considered a calcium silicate hydrate forms. The development of hydrogen gas gives the mass macroporosity. The rising mass is typically contained within a mold. After rising, the mass is permitted to stiffen in the mold forming a semiplastic body which has low strength, but which will keep together after removal from the mold.
After a desired degree of stiffness is achieved and the body is removed from the mold, the body may typically be divided or cut by wires into separate elements having the desired shape, such as building blocks or larger building panels. The divided body is positioned in an autoclave where it is steam cured at high pressure and high temperature to obtain suitable strength. The body is then advanced to a separation station where the adjacent building blocks or panels are separated from one another. The blocks are packaged, such as onto pallets for storage and transportation.
Because the building blocks are divided from the solid mass of material, the blocks are solid generally rectangular bodies. The solid blocks are still relatively lightweight, although somewhat awkward to handle by the mason. The blocks may come in various conventional block sizes, such as typically about two feet in length with various widths and heights.
In most block walls, including those formed of aerated concrete blocks, it may also be desirable to add vertical reinforcements. This may be so especially in coastal areas or other locations susceptible to high winds. For example, it may be desired to have a vertical reinforcing member, such as a reinforcing bar, periodically secured to or secured within the wall and extending from the bottom of a block wall to the top of the wall to meet certain building codes.
To provide the periodic vertical reinforcing, one conventional practice is to drill a passageway through the blocks upon completion of the entire height of the wall to receive a vertical reinforcing member. Such a process is not only awkward, but is also time consuming. Alternately, a slot may be cut into a surface of the wall to receive a vertical reinforcing member. Such, conventional ad hoc reinforcing techniques carried out at the building site may not always yield consistent results. Moreover, the time needed for such vertical reinforcing measures increases the costs of construction using conventional solid aerated concrete blocks.
In view of the foregoing background, it is therefore an object of the present invention to provide an efficient and cost effective method for making aerated concrete blocks of a type that will speed construction at the building site, and which also facilitate vertical reinforcement of walls formed from the blocks.
This and other objects, features and advantages in accordance with the invention are provided by a method for making aerated concrete blocks wherein the blocks are formed to have one or more passageways extending therethrough. More particularly, the method may include dispensing materials for making aerated concrete into a mold and allowing the materials to rise and stiffen into a body. The body may be divided into an array of blocks and then cured. At least one passageway may be formed extending through each block, such as formed by drilling, for example. Each block may have a plurality of spaced apart passageways formed or drilled therein, and each passageway may have a circular cylindrical shape. The passageways provide easier grasping by the mason, reduce the weight without significantly compromising strength, and may be aligned in a wall during construction at a building site to facilitate the placement of vertical reinforcing members in the wall.
The drilling, for example, may comprise providing a plurality of drills and causing relative movement between the drills and at least one group of blocks to simultaneously drill the one or more passageways in each block. The step of causing relative movement may include grasping and moving the group of blocks along a predetermined path while the plurality of drills remain stationary. In one embodiment, the drills are directed substantially vertically upward, and the predetermined path is substantially vertical so that waste from drilling will fall by gravity for recycling. Recycling of the waste also reduces the costs of production, since less virgin materials are then required.
Another important advantage relates to the shape of each cured block formed in accordance with the method of the present invention. In particular, each block may have a generally rectangular shape defining a length between opposing ends, a width between opposing sides, and a height between a top and bottom. The at least one passageway may comprise first and second passageways, for example, extending in the height direction between the top and bottom. In addition, each first and second passageway may be centered inwardly from the opposing sides and also have an axis centered inwardly from a respective adjacent end a distance of about one-half the width. This configuration allows for alignment of the passageways in adjacent blocks, especially at wall corners.
The length of each block may be in a range of about 16 to 24 inches, the width may be in a range of about 8 to 12 inches, and the height may be in a range of about 8 to twelve inches. The length may also range from about 2 to 3 times the width for some embodiments. In one variation, a third passageway may be provided to extend between the bottom and the top. This third passageway is preferably centered inwardly from opposing sides and inwardly from opposing ends.
The method may also include packaging the blocks after drilling for storage and transportation. For example, the packaging may comprise packaging a group of blocks on each of a plurality of pallets. The method may also comprise mixing the materials prior to dispensing the materials into the mold. The materials may comprise sand or ash, cement, lime, water, and an aeration agent, such as aluminum.
The method may also include releasing the body from the mold prior to dividing the body, and trimming at least one side of the body during the dividing. The dividing and/or trimming may be carried out using cutting wire to form a series of laterally extending and vertically extending cuts through the body.
The curing may comprise subjecting the array of blocks to an elevated temperature and an elevated pressure for a predetermined time. For example, the curing may be carried out in an autoclave using steam. In addition, the method may also include separating the blocks after curing.